Expandable sheath

ABSTRACT

Disclosed herein are expandable introducer sheaths and methods of making and using the same. The sheaths minimize trauma to a patient&#39;s vasculature by allowing for temporary expansion of a portion of the sheath to accommodate passage of a delivery system for a cardiovascular device, then return to a non-expanded state after the passage of the device. The sheath includes an elongated annular member having longitudinally extending channels that facilitate the sheath&#39;s temporary expansion. The channels are positioned in such a way that, upon expansion, they enable the movement of protruding contact surfaces toward the inner and outer surfaces of the annular member, reducing friction between the surface and the passing device. Some embodiments of the expandable sheath include an elastic outer layer that pushes the protruding contact surfaces back towards their original positions after the passage of the device.

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 62/449,454, filed Jan. 23, 2017, which is incorporatedherein by reference.

FIELD

The present application is directed to a sheath for use withcatheter-based technologies for repairing and/or replacing heart valves,as well as for delivering an implant, such as a prosthetic valve to aheart via the patient's vasculature.

BACKGROUND

Endovascular delivery catheter assemblies are used to implant prostheticdevices, such as a prosthetic heart valve, at locations inside the bodythat are not readily accessible by surgery or where less invasivesurgery is desirable. For example, aortic, mitral, tricuspid, and/orpulmonary prosthetic valves can be delivered to a treatment site usingminimally invasive surgical techniques, including transcatheter deliverymethods.

An introducer sheath can be used to safely introduce a deliveryapparatus into a patient's vasculature (e.g., the femoral artery). Anintroducer sheath generally has an elongated sleeve that is insertedinto the vasculature and a housing that contains one or more sealingvalves that allow a delivery apparatus to be placed in fluidcommunication with the vasculature with minimal blood loss. Aconventional introducer sheath typically requires a tubular loader to beinserted through the seals in the housing to provide an unobstructedpath through the housing for the prosthetic implant, such as a heartvalve mounted on a balloon catheter. A conventional loader extends fromthe proximal end of the introducer sheath, and therefore decreases theavailable working length of the delivery apparatus that can be insertedthrough the sheath and into the body.

Conventional methods of accessing a vessel, such as a femoral artery,prior to introducing the delivery system include dilating the vesselusing multiple dilators or sheaths that progressively increase indiameter. This repeated insertion and vessel dilation can increase theamount of time the procedure takes, as well as the risk of damage to thevessel.

Radially expanding intravascular sheaths reduce the overall profile ofthe sheath to reduce risk of damage to the vessel. Such sheaths tend tohave complex mechanisms, such as ratcheting mechanisms that maintain theshaft or sheath in an expanded configuration once a device with a largerdiameter than the sheath's original diameter is introduced.

However, delivery and/or removal of prosthetic devices and othermaterial to or from a patient still poses a risk to the patient.Furthermore, accessing the vessel remains a challenge due to therelatively large profile of the delivery system that can causelongitudinal and radial tearing of the vessel during insertion. Thedelivery system can additionally dislodge calcified plaque within thevessels, posing an additional risk of clots caused by the dislodgedplaque. The addition of radially expanding properties can also hinder apractitioner's ability to push the sheath without it bending or kinking.Thus, there remains a need for further improvements in introducersheaths for endovascular systems used for implanting heart valves andother prosthetic devices.

SUMMARY

Disclosed herein are expandable introducer sheaths and methods of makingand using the same. The sheaths are adapted to temporarily expand aportion of the sheath to allow for the passage of a delivery system fora cardiovascular device, then return to a non-expanded state after thepassage of the system. The sheath includes an elongated annular memberthrough which the cardiovascular device and its delivery system pass.The annular member has longitudinally extending channels that facilitatethe sheath's expansion. The channels are positioned in such a way that,upon expansion, they enable the movement of longitudinally extendingcontact surfaces toward the inner and outer surfaces of the annularmember, reducing friction between the surface and the passing device.Some embodiments of the expandable sheath include an elastic outer layerthat pushes the contact surfaces back towards their original positionsafter the passage of the device. Methods of making an expandable sheathtip are also included.

Disclosed herein are expandable sheaths including an elongated annularmember that has an inner and outer surface. The annular member alsoinclude a bridge member extending between opposing first and second basemembers spaced around the circumference of the annular member. Theexpandable sheath is radially movable between an expanded state and anon-expanded state. In the non-expanded state, the annular memberincludes a first and second longitudinally extending channel. The firstlongitudinally extending channel is defined between the bridge memberthe first base member and extends inwardly from the outer surface of thesheath towards the annular member's longitudinal axis. The secondlongitudinally extending channel is defined between the bridge memberand the second base member and extends outwardly from the inner surfaceof the sheath away from the longitudinal axis of the annular member. Inthe expanded state, the bridge member extends in a direction around thecircumference of the annular member increasing a distance between thefirst and second base members.

In some embodiments of the expandable sheath, the expanded diameter ofthe annular member is greater than the non-expanded diameter of theannular member.

In some embodiments of the expandable sheath the orientation of thefirst and second base members changes when the annular member movesbetween the expanded and non-expanded state. For example, theorientation of the first and second base members can rotate about alongitudinal axis of each of the respective base members when theannular member is moved between the expanded and non-expanded state.

Some embodiments of the expandable sheath include the first and secondbase members having a contact edge that defines the inner diameter ofthe annular member in the expanded state.

In some embodiments, the bridge member extends in a direction around acircumference of the annular member in the expanded state. For example,the first and second base members can extend in a direction around acircumference of the annular member in the expanded and non-expandedstate, and at least a portion of the bridge member can extend in adirection towards the longitudinal axis of annular member in thenon-expanded state and around the circumference of the annular member inthe expanded state.

In some embodiments the first and second base members define arectilinear shape in cross-section. The bridge member can define anS-shape in cross-section. In some embodiments, the bridge member candefine an arcuate shape in cross-section.

Some embodiments of the expandable sheath includes an outer layerextending over the annular member, the outer layer can comprise amaterial having a higher elastic modulus than the annular member and theannular member can comprise a material having greater lubricity than theouter layer.

Also disclosed is an expandable sheath including an elongated annularmember movable between a non-expanded and expanded state. The annularmember includes base members spaced around a circumference of theannular member, and bridge members extending between opposing pairs ofbase members. In the non-expanded state the annular member includesinwardly and outwardly extending channels that extend towards and awayfrom the longitudinal axis of the annular member, respectively. Theinwardly and outwardly extending channels can be defined between thebase and bridge members. In the expanded state the diameter of theannular member is increased and a spacing between opposing based membersis increased from the non-expanded state diameter and spacing.

In some embodiments of the expandable sheath, one inwardly extendingchannel and one outwardly extending channels is provided at opposingends of a corresponding one of the bridge members. In some embodiments,in the expanded state the depth of each of the inwardly and outwardlyextending channels, in a radial direction, is decreased compared to adepth of each of the channels in the non-expanded state.

In some embodiments of the expandable sheath the base members include afirst, second and third base member and the bridge members include afirst and second bridge member. The first bridge member extends betweenthe first and second base members, and the second bridge member extendsbetween the second and third base members.

Also disclosed is a method of making an expandable sheath. The methodincludes coextruding a tube comprising a first material and a secondmaterial. The first material defines the elongated annular member havingan outer surface and an inner surface. The first material furtherdefines a first and second set of longitudinally extending channels. Thefirst set of longitudinally extending channels extend inwardly from anouter surface of the elongated member towards the longitudinal axis ofthe annular member. The second set of longitudinally extending channelsextend outwardly from an inner surface of the annular member away fromthe longitudinal axis. The second material defines a first set oflongitudinally extending ribbons extending within the first set ofchannels and a second set of longitudinally extending ribbons extendingwithin the second set of channels. Each ribbon of a selected set ispositioned circumferentially between ribbons of the other set.

In some embodiments, the method of making an expandable sheath canfurther include coextruding a third material in contact with a portionof the first material and a portion of the second material, wherein thethird material adheres to both the first material to the secondmaterial. The third material can be located between a portion of thefirst and second material within the first and second set of channels.

In some embodiments, the method of making an expandable sheath canfurther include adding a taper tube to the coextrusion.

In some embodiments, the method of making an expandable sheath canfurther include removing the second material and exposing the first andsecond set of longitudinally extending channels upon removal of thesecond sacrificial material.

In some embodiments, the method can further include covering the annularmember with an outer layer comprising a material having a higher elasticmodulus than the annular member.

Also disclosed is a method of delivering a cardiovascular prostheticdevice. The method includes positioning an expandable sheath at animplantation site within the vascular system of a patient, introducing aprosthetic device into a lumen of the expandable sheath, advancing acardiovascular prosthetic device through the lumen of the expandablesheath, exerting a radially outward force on an inner surface of thesheath with the cardiovascular prosthetic device, wideninglongitudinally extending channels provided circumferentially around theinner and outer surfaces of the sheath and moving longitudinallyextending contact surfaces toward the inner and outer surfaces of thesheath, thereby expanding a portion of the sheath a a location of theradially outward force. The method further includes at least partiallycollapsing the expanded portion of the sheath after the device haspassed through the expanded portion. In some embodiments, thecardiovascular prosthetic device is a prosthetic heart valve.

In some embodiments, the method of delivering a cardiovascularprosthetic device can further include moving the contact surfaces awayfrom the inner and outer surfaces of the annular member after passage ofthe cardiovascular prosthetic device using an outer layer of theexpandable sheath.

Also disclosed is a method of making a distal tip of an expandablesheath. The method includes pinching a portion of the distal end of atube to create a longitudinally extending outer crease, folding thepinched portion over an outer surface of a distal end of the tube in acircumferential direction to create a longitudinally extending flapbounded by the outer crease and a longitudinally extending inner crease,cutting the inner crease of the longitudinally extending flap in alongitudinal direction from the distal edge of the tube to a proximallyspaced point along the longitudinal axis of the tube to create alongitudinally extending inner edge, cutting the longitudinallyextending flap at the proximally spaced point in a circumferentialdirection from the outer crease to the longitudinal cut at the innercrease, extending the inner edge of the longitudinally extending flap ina circumferential direction around the outer surface of the distal endof the tube, and adhering the cut inner crease to the outer surface ofthe distal end of the tube to create the distal tip. Some embodiments ofthe method further include covering the cut distal end of the tube withan outer jacket and reflowing the tube with the outer jacket to createthe sealed distal tip.

DESCRIPTION OF DRAWINGS

In the drawings, like reference numbers and designations in the variousdrawings indicate like elements.

FIG. 1 is an elevation view of an expandable sheath along with anendovascular delivery system for implanting a prosthetic heart valve.

FIG. 2A shows a cross sectional view of an example expandable sheath inthe non-expanded state.

FIG. 2B shows the expandable sheath of FIG. 2A in the expanded state.

FIG. 3A shows a cross sectional view of an example expandable sheath inthe non-expanded state.

FIG. 3B shows the expandable sheath of FIG. 3A in the expanded state.

FIG. 4A shows a cross sectional view of an example expandable sheath inthe non-expanded state.

FIG. 4B shows the expandable sheath of FIG. 4A in the expanded state.

FIG. 5A shows a cross sectional view of an example expandable sheath inthe non-expanded state.

FIG. 5B shows the expandable sheath of FIG. 5A in the expanded state.

FIG. 6A shows a cross sectional view of an example an expandable sheathin the non-expanded state.

FIG. 6B shows the expandable sheath of FIG. 6A in the expanded state.

FIG. 7A shows a cross sectional view of an example expandable sheathduring an intermediate processing step.

FIG. 7B shows the expandable sheath of FIG. 7A in a non-expanded state,after removal of a sacrificial material.

FIG. 7C shows the expandable sheath of FIG. 7B in the expanded state.

FIG. 8 shows a perspective view of an expandable sheath.

FIG. 9 shows a method of making a distal tip of an expandable sheath.

DETAILED DESCRIPTION

The following description of certain examples of the inventive conceptsshould not be used to limit the scope of the claims. Other examples,features, aspects, embodiments, and advantages will become apparent tothose skilled in the art from the following description. As will berealized, the device and/or methods are capable of other different andobvious aspects, all without departing from the spirit of the inventiveconcepts. Accordingly, the drawings and descriptions should be regardedas illustrative in nature and not restrictive.

For purposes of this description, certain aspects, advantages, and novelfeatures of the embodiments of this disclosure are described herein. Thedescribed methods, systems, and apparatus should not be construed aslimiting in any way. Instead, the present disclosure is directed towardall novel and nonobvious features and aspects of the various disclosedembodiments, alone and in various combinations and sub-combinations withone another. The disclosed methods, systems, and apparatus are notlimited to any specific aspect, feature, or combination thereof, nor dothe disclosed methods, systems, and apparatus require that any one ormore specific advantages be present or problems be solved.

Features, integers, characteristics, compounds, chemical moieties, orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract, and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The invention is notrestricted to the details of any foregoing embodiments. The inventionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract, and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

It should be appreciated that any patent, publication, or otherdisclosure material, in whole or in part, that is said to beincorporated by reference herein is incorporated herein only to theextent that the incorporated material does not conflict with existingdefinitions, statements, or other disclosure material set forth in thisdisclosure. As such, and to the extent necessary, the disclosure asexplicitly set forth herein supersedes any conflicting materialincorporated herein by reference. Any material, or portion thereof, thatis said to be incorporated by reference herein, but which conflicts withexisting definitions, statements, or other disclosure material set forthherein will only be incorporated to the extent that no conflict arisesbetween that incorporated material and the existing disclosure material.

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” include plural referents unless the context clearlydictates otherwise. Ranges may be expressed herein as from “about” oneparticular value, and/or to “about” another particular value. When sucha range is expressed, another aspect includes from the one particularvalue and/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another aspect. It will befurther understood that the endpoints of each of the ranges aresignificant both in relation to the other endpoint, and independently ofthe other endpoint.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where said event or circumstance occurs and instances where itdoes not.

Throughout the description and claims of this specification, the word“comprise” and variations of the word, such as “comprising” and“comprises,” means “including but not limited to,” and is not intendedto exclude, for example, other additives, components, integers or steps.“Exemplary” means “an example of” and is not intended to convey anindication of a preferred or ideal aspect. “Such as” is not used in arestrictive sense, but for explanatory purposes.

Disclosed herein are expandable introducer sheaths and methods of makingand using the same. As will be described in further detail below, theexpandable sheaths 1 are adapted to allow for temporary expansion of aportion of the sheath to accommodate the passage of a delivery systemfor a cardiovascular device, then return to a non-expanded state, or“recover” after the passage of the delivery system and device.

FIG. 1 illustrates a sheath 1 according to the present disclosure in usewith a representative delivery apparatus 210 for delivering a prostheticdevice 212, such as a tissue heart valve, to a patient. The apparatus210 can include a steerable guide catheter 214 (also referred to as aflex catheter), a balloon catheter 216 extending through the guidecatheter 214, and a nose catheter 218 extending through the ballooncatheter 216. The guide catheter 214, the balloon catheter 216, and thenose catheter 218 in the illustrated embodiment are adapted to slidelongitudinally relative to each other to facilitate delivery andpositioning of the valve 212 at an implantation site in a patient'sbody, as described in detail below. Generally, a sheath 1 is insertedinto a vessel, such as the transfemoral vessel, passing through the skinof patient, such that the distal end of the sheath 1 is inserted intothe vessel. Sheath 1 can include a hemostasis valve at the opposite,proximal end of the sheath. The delivery apparatus 210 can be insertedinto the sheath 1, and the prosthetic device 212 can then be deliveredand implanted within patient.

The expandable introducer sheath 1 is adapted to allow for temporaryradial expansion of a portion of the sheath to accommodate the passageof a delivery system for a cardiovascular device (e.g., prosthetic heartvalve 212) and to then return to a non-expanded state after the passageof the delivery system with its prosthetic device. The expandable sheath1 includes an elongated annular member 10 through which the deliverysystem and prosthetic heart valve 212 pass. As will be described in moredetail below, the annular member 10 of the expandable sheath 1 caninclude longitudinally extending channels 12, 14 that facilitate thesheath's expansion for passage of the prosthetic heart valve 212. Thechannels 12, 14 are positioned such that upon expansion of the annularmember 10 certain contact surfaces 22, 24 are brought into contact withadjacent surfaces of the delivery apparatus 210, thereby reducingfriction between the annular member 10 and the passing structure. Insome embodiments, the radial expansion of the expandable annular member10 at any given portion along its length is due to the ability of base20 and/or bridge members 30 of the annular member 10 to rotate. Therotation of these sections reduces the surface/contact area of theannular member 10 thereby reducing friction with the passing structure.The expandable sheath 1 can include an elastic outer layer 50. In someembodiments, the outer layer 50 can compress the annular member 10towards a non-expanded configuration.

FIGS. 2A and 2B show a cross-section of an example expandable sheath 1in an expanded (FIG. 2A) and a non-expanded (FIG. 2B) state. Thenon-expanded sheath 1 includes an inner annular member 10 and an outerlayer 50. The outer layer 50 can be constructed from an elastic materialthat allows for temporary radial expansion of a portion of the outerlayer 50 corresponding to the temporary radial expansion of the annularmember 10 to accommodate the passage of the delivery system for acardiovascular device (e.g., prosthetic heart valve 212). After passageof the delivery system with its prosthetic device, the annular member 10and outer layer 50 return to a non-expanded state (FIG. 2B). Asillustrated in FIG. 2A, the annular member 10 includes a plurality ofbase members 20 arranged around the circumference of the annular member10 and bridge members 30 extending between opposing pairs of basemembers 20 (e.g., base member 20 a and base member 20 b). As illustratedin FIG. 2A, the base members 20 can define a rectilinear shape incross-section. The base members 20 can include an outer edge that definethe outer surface/diameter 16 of the annular member 10 and an inner edgethat define the inner surface/diameter 18. Base members 20 can includeside walls 15 that extend radially between the inner and outer edges. Asillustrated in FIG. 2A, the outer edge has a longer length (around thecircumference of the annular member 10) than the inner edge. The sidewalls 15 can meet the inner and outer edges at a curve (illustrated) orangle. The side walls 15 can terminate at the bridge member 30. Asprovided in FIG. 2A, the side walls 15 can meet the bridge members 30 ata curve. In other example annular members 10 (see e.g., FIG. 6A) theside wall of the base member 20 can meet the bridge member 30 at astraight or angled edge/joint. It is further contemplated that the basemembers 20 can define any regular or irregular shape in cross-sectionincluding, for example, square, rectangle, trapezoidal, circular, andoval. Likewise, bridge members 30 can define any regular or irregularshape. As provided in FIG. 2A, in the unexpanded state the bridgemembers 30 define a generally S-shape cross-section. That is, incross-section, the bridge members 30 of FIG. 2A can include a relatively(radially) elongate shape that extends between bends (at joints 32)where the bridge member 30 couples to the adjacent base member 20. Thebends bracket the ends of the elongate portion and serve as theconnection to either the radially inward corner or radially outwardcorner of adjacent base members. The elongate portion of the bridgemember 30 can also widen in the outward radial direction. As will beexplained in more detail below, during expansion of the annular member10 the shape of the base member 20 and/or bridge member 30 changes orotherwise deforms.

As illustrated in FIG. 2A, in the non-expanded state, the annular member10 includes longitudinally extending channels 12, 14. Inward extendingchannels 12 extend radially inward from the outer surface/diameter 16 ofthe annular member 10 towards its longitudinal axis 11. The inwardextending channels 12 are defined between a base member 20 and anadjacent bridge member 30. The outward extending channels 14 extendradially outward from the inner surface/diameter 18 of the annularmember 10 in a radial direction away from the longitudinal axis 11 andare similarly defined between a base member 20 and an adjacent bridgemember 30.

The inward and outward extending channels 12, 14 alternate in inwardversus outward directionality, such that each channel of a selectedset/direction is positioned circumferentially between two channels ofthe other set/direction (i.e., an inward extending channel 12 isposition circumferentially between two outward extending channels 14).

As depicted in FIG. 2A, the inward and outward extending channels 12, 14extend radially with respect to the longitudinal axis 11 of the annularmember 10. For example, the centerline (c) of each of the inward andoutward extending channels 12, 14 can create a 90-degree angle (a) witha line tangent to the diameter of the annular member 10 proximate theopening of the channel.

The inward and outward extending channels 12, 14 extend a certain depth(d) into the wall thickness (t) of the annular member 10. For example,as illustrated in FIG. 2A, the inward and outward extending channels 12,14 can have a depth greater than 50% of the wall thickness (t) of theannular member 10. Though not illustrated, it is contemplated that thedepth of the inward and outward extending channels 12, 14 can also varyaround the annular member 10.

The inward and outward extending channels 12, 14 can also define a width(w) measured along the length/depth of the channel. The width (w) can bedefined between the sidewall of the corresponding bridge member 30 andbase member 20, i.e., side wall 13 and side wall 15. As illustrated inFIG. 2A, the width (w) of each channel can be uniform around the annularmember 10. It is also contemplated that the width (w) of differentchannels can vary around the annular member 10. The width (w) of theinward and outward extending channels 12, 14 can remain constant (seeFIG. 2A) or vary along the depth (d) of the channel.

The shape of the inward and outward extending channels 12, 14 can remainconstant or vary around the annular member 10. As depicted in FIG. 2A,each of the inward and outward extending channels 12, 14 have twosubstantially parallel and straight sides (defined by side wall 13 andside wall 15) that terminate at a rounded end 19. It is contemplatedthat the shape of inward and outward extending channels 12, 14 candefine any regular or irregular shape and that the shape of each inwardand outward extending channel 12, 14 can vary (or remain constant)around the annular member 10.

In the embodiment shown in FIG. 2A, the inward and outward extendingchannels 12, 14 are evenly distributed around the circumference of theannular member 10 and are similar in size and shape. While it iscontemplated that the size and spacing of the base members 20, bridgemembers 30 and corresponding inward and outward extending channels 12,14 can vary, even spacing and uniform size and shape help to preventtearing of the annular member 10 during expansion. For example, duringexpansion (shown in FIG. 2B) tension is distributed to many pointsaround the circumference of the annular member 10 and not focused at asingle location. This distribution of tension reduces the risk oftearing the annular member 10.

As described above, the annular member 10 and elastic outer layer 50 ofthe sheath 1 are designed to locally expand as the prosthetic device 212is passed through the interior lumen of the sheath 1 and thensubstantially return to their original shape once the prosthetic devicehas passed through that portion of the sheath. That is, in thenon-expanded state the outer diameter of the annular member 10 and outerlayer 50 can be substantially constant across the length of the sheath 1from the proximal end 3 to the distal end 5. As the prosthetic device212 passes through the interior lumen of the sheath 1, the portion ofthe annular member 10 and outer layer 50 proximate the prosthetic device212 expand radially, with the remaining length/portion of the annularmember 10 and outer layer 50 in a substantially non-expanded state. Oncethe device has passed through a portion of the lumen of the sheath 1,that portion of the sheath 1 can substantially return to its originalshape and size. FIG. 2B illustrates the annular member 10 and outerlayer 50 in an expanded state. In the expanded state the outer diametersof the annular member 10 and elastic outer layer 50 are greater than thenon-expanded diameters of the annular member 10 and outer layer 50.

To achieve expansion, the orientation of the base members 20 and bridgemembers 30 changes. As illustrated in FIG. 2B, the base members 20rotate during expansion of the annular member 10. For example, the basemembers 20 rotate with respect to the central axis of each correspondingbase member 20. Similarly, the bridge members 30 rotate and flex atjoints 32 to extend in a direction around the circumference of theannular member 10, thereby increasing the distance/spacing betweenadjacent base members 20 and widening/changing the shape of each of theintervening inward and outward extending channels 12, 14. The bridgemembers 30 can be constructed from a flexible material to accommodateflexing at joints 32 and/or lengthening/deformation during expansion ofthe annular member 10 and then substantially return to the original,non-expanded shape/configuration. The base members 20 can be constructedfrom a same or different material than the bridge members 30.Accordingly, it is also contemplated that the base members 20 can flexand deform during expansion and contraction of the annular member 10.

As illustrated in FIG. 2B, in the expanded state the orientation of thebase members 20 and bridge members 30 changes. Contact surfaces 22, 24provided on the base members 20 now define the inner and outer diametersof the annular member 10, respectively. In the expanded state, thecontact surfaces 24 define the inner diameter of the outer layer 50. Thecontact surfaces 22 extend towards the interior of the annular member 10and reduce the contact surface area between the annular member 10 andthe passing device, thereby lowering the coefficient offriction/resistance between the inner surface 18 of the annular member10 and the passing device. The contact surfaces 22, 24 can definerounded/curved ends 26 or linear/angled ends 28 when viewed incross-section. For example, the contact surfaces 22, 24 of the expandedembodiments shown in FIGS. 2B, 3B, 4B, 5B and 6C include rounded ends 26in cross-section. In another example, the expanded annular memberdepicted in FIG. 7B includes both angled ends 28 and rounded ends 26 atthe contact surfaces 22, 24. Referring back to FIG. 2B, the shape of therounded ends 26, including the radii of curvature, can be constantacross all base members 20 of the annular member 10. It is alsocontemplated that the shape of the rounded ends 26/contact surfaces 22,24 may vary between base members 20, and vary between contact surface 22and contact surface 24 of the same base member 20.

In transition back to the non-expanded state, the base members 20 andbridge members 30 move back to their original configuration/orientation.The transition back to the non-expanded state can be facilitated by theinclusion of an elastic outer layer 50 that extends over the elongatedannular member 10. The outer layer 50 comprises a material having ahigher elastic modulus than the annular member 10, which enables theouter layer 50 to force the annular member 10 back into the non-expandedstate after passage of the cardiovascular device. The annular member 10can be made of a more lubricious material than the outer layer 50. Forexample, the outer layer 50 can be made of, or incorporate,polyurethane, silicone, and/or rubber, and the annular member 10 can bemade of, or incorporate, high density polyethylene,polytetrafluoroethylene, and/or other fluoropolymers.

FIGS. 3A and 3B depict another example sheath 1 including an annularmember 10 and elastic outer layer 50. The annular member 10 has aplurality of base members 20 arranged around the circumference of theannular member 10 and bridge members 30 extending between opposing pairsof base members 20. As illustrated in FIG. 3A, the base members 20 andbridge members 30 can define a curvilinear shape in cross-section. Forexample, as depicted in FIG. 3A, the base member 20 can define anelongated portion extending around the outer surface/diameter 16 of theannular member and terminating in a rounded end 26 contact surface 24.The bridge 30 can define an elongated member having substantially linearand parallel sides and terminating at a curved end proximate the innersurface/diameter 18 of the annular member 10.

Similar to the annular member 10 depicted in FIG. 2A, in thenon-expanded state the annular member 10 of FIG. 3A includeslongitudinally extending channels 12, 14 defined between a bridge member30 and adjacent base member 20 alternating in inward versus outwarddirectionality around the circumference of the annular member 10. Theinward extending channels 12 extend inward from the outersurface/diameter 16 of the annular member 10 and the outward extendingchannels 14 extend outward from the inner surface/diameter 18 of theannular member 10. The inward and outward extending channels 12, 14 canextend inward or outward from the inner/outer surface 16, 18 at anangle, e.g., at an angle other than 90-degrees (with respect to a linetangent to the diameter of the annular member 10 proximate the openingof the channel).

As described above, the annular member 10 and the elastic outer layer 50of the sheath 1 are designed to locally expand in a radial directionbetween a non-expanded and an expanded state as the prosthetic device212 is passed through the interior lumen of the sheath 1. FIG. 3Billustrates the annular member 10 and outer layer 50 in an expandedstate. The orientation and/or shape of the base members 20 and bridgemembers 30 of the annular member 10 change during expansion. Asillustrated in FIG. 3B, the base members 20 extend and elongate in adirection around the circumference of the annular member 10 whentransitioned to the expanded state. The bridge members 30 change inorientation during expansion. In the non-expanded state the bridgemembers 30 extend is a direction toward/angled with respect to thelongitudinal axis 11/the interior of the annular member 10. Uponexpansion of the annular member 10 the bridge members 30 rotate,elongate and/or extend in a direction around the circumference of theannular member 10. For example, the bridge members 30 can flex at joints32 to facilitate their change in orientation with respect to the basemembers 20. Upon expansion of the annular member 10, thedistance/spacing between adjacent base members 20 increases, wideningand changing the shape of the intervening inward and outward extendingchannels 12, 14 and increasing the overall diameter of the annularmember 10 and the outer layer 50.

As illustrated in FIG. 3B, in the expanded state the contact surfaces 22provided on the base member 20 and/or bridge member 30 define the innerdiameter of the annular member 10. Likewise, the contact surface 24defines the outer diameter of the annular member 10, and thecorresponding inner diameter of the outer layer 50 in the expandedstate. The outside surface of the outer layer 50 defines the outermostdiameter of the combined annular member 10/outer layer 50. Contactsurfaces 22 reduce the contact surface area between the annular member10 and the passing device, thereby lowering the coefficient offriction/resistance between the inner surface 18 and the passing device.

FIGS. 4A and 4B depict an example sheath 1 including an annular member10 and elastic outer layer 50. The annular member 10 has four basemembers 20 arranged around the circumference of the annular member 10and four corresponding bridge members 30 extending between opposingpairs of base members 20. In the non-expanded state, the base members 20and bridge members 30 can define a curvilinear shape in cross-section.For example, as depicted in FIG. 4A, the base members 20 can define twoarcuate portions having substantially similar shape terminating in twosubstantially linear portions extending in a radial direction withrespect to the annular member 10. The bridge members 30 can define anS-shape in cross-section.

Similar to the annular member 10 depicted in FIGS. 2A and 3A, in thenon-expanded state the annular member 10 of FIG. 4A includeslongitudinally extending channels 12, 14 defined between a bridge member30 and adjacent base member 20 alternating in inward versus outwarddirectionality around the circumference of the annular member 10. Theinward and outward extending channels 12, 14 extend radially withrespect to the longitudinal axis 11 of the annular member 10. Forexample, the centerline of each of the inward and outward extendingchannels 12, 14 creates a 90-degree angle with a line tangent to thediameter of the annular member 10 proximate the opening of the channel.

As described above, the annular member 10 and the elastic outer layer 50are designed to locally expand in a radial direction between anon-expanded and an expanded state as the prosthetic device 212 ispassed through the interior lumen of the sheath 1. FIG. 4B illustratesthe annular member 10 and outer layer 50 in an expanded state. Theorientation and/or shape of the base members 20 and bridge members 30 ofthe annular member 10 change during expansion. As illustrated in FIG.4B, the base members 20 extend and/or elongate in a direction around thecircumference of the annular member 10 when transitioned to the expandedstate. The bridge members 30 also change in orientation and/or shapeduring expansion. In the non-expanded state the bridge members 30 extendis a direction toward the longitudinal axis 11/the interior of theannular member 10. Upon expansion of the annular member 10 the bridgemembers 30 rotate, elongate and/or extend in a direction around thecircumference of the annular member 10. For example, the bridge members30 can flex at joints 32 to facilitate their change in orientation withrespect to the base members 20. Upon expansion of the annular member 10,the distance/spacing between adjacent base members 20 increases,widening and changing the shape of the intervening inward and outwardextending channels 12, 14 and increasing the overall diameter of thesheath and the outer layer 50.

As illustrated in FIG. 4B, in the expanded state the contact surfaces 22provided on the base members 20 define the inner diameter of the annularmember 10. Likewise, the contact surface 24 defines the outer diameterof the annular member 10, and the corresponding inner diameter of theouter layer 50 in the expanded state. It is contemplated that a portionof the inner surface 16 and outer surface 18 of the base member 20 canalso define the inner and outer diameter of the annular member 10 in theexpanded state. Contact surfaces 22 reduce the contact surface areabetween the annular member 10 and the passing device, thereby loweringthe coefficient of friction/resistance between the annular member andthe passing device.

FIGS. 5A and 5B depict another example sheath 1 including an annularmember 10 and elastic outer layer 50. The annular member 10 has eighteenbase members 20 arranged around the circumference of the annular member10 and eighteen corresponding bridge members 30 extending betweenopposing pairs of base members 20. In the non-expanded state, the basemembers 20 and bridge members 30 can define a curvilinear shape incross-section. For example, as depicted in FIG. 5A, the base members 20can define a semi-rectangular shape. The bridge members 30 can define anS-shape in cross-section.

Similar to the annular members 10 depicted in FIGS. 2A, 3A and 4A, inthe non-expanded state the annular member 10 of FIG. 5A includeslongitudinally extending channels 12, 14 defined between a bridge member30 and adjacent base member 20 alternating in inward versus outwarddirectionality around the circumference of the annular member 10. Theinward and outward extending channels 12, 14 extend radially withrespect to the longitudinal axis 11 of the annular member 10. Forexample, the centerline of each of the inward and outward extendingchannels 12, 14 creates a 90-degree angle with a line tangent to thediameter of the annular member 10 proximate the opening of the channel.

As described above, the annular member 10 and the elastic outer layer 50are designed to locally expand in a radial direction between anon-expanded and an expanded state as the prosthetic device 212 ispassed through the inner lumen of the sheath 1. FIG. 5B illustrates theannular member 10 and outer layer 50 in an expanded state. Theorientation and/or shape of the base members 20 and bridge members 30 ofthe annular member 10 change during expansion. As illustrated in FIG.5B, the base members 20 extend and/or elongate in a direction around thecircumference of the annular member 10 when transitioned to the expandedstate. The bridge members 30 also change in orientation and/or shapeduring expansion. In the non-expanded state the bridge members 30 extendin a direction toward the longitudinal axis 11/the interior of theannular member 10. Upon expansion of the annular member 10 the bridgemembers 30 rotate, elongate and/or extend in a direction around thecircumference of the annular member 10. For example, the bridge members30 can flex at joints 32 to facilitate their change in orientation withrespect to the base members 20. Upon expansion of the annular member 10,the distance/spacing between adjacent base members 20 increases,widening and changing the shape of the intervening inward and outwardextending channels 12, 14 and increasing the overall diameter of theannular member 10 and the outer layer 50.

As illustrated in FIG. 5B, in the expanded state the contact surfaces 22provided on the base members 20 define the inner diameter of the annularmember 10. Likewise, the contact surface 24 defines the outer diameterof the annular member 10, and the corresponding inner diameter of theouter layer 50 in the expanded state. Contact surfaces 22 reduce thecontact surface area between the annular member 10 and the passingdevice, thereby lowering the coefficient of friction/resistance betweenthe annular member and the passing device.

FIGS. 6A and 6B depict another example sheath 1 including an annularmember 10 and elastic outer layer 50. The annular member 10 has basemembers 20 arranged around the circumference of the annular member 10and corresponding bridge members 30 extending between opposing pairs ofbase members 20.

In the non-expanded state, the base members 20 and bridge members 30 candefine a curvilinear shape in cross-section. For example, as depicted inFIG. 6A, the base members 20 define a wedge shape. The bridge members 30define an arcuate/curved shape in cross-section.

Similar to the annular members 10 depicted in FIGS. 2A, 3A, 4A and 5A,in the non-expanded state the annular member 10 of FIG. 6A includeslongitudinally extending channels 12, 14 defined between a bridge member30 and adjacent base member 20 alternating in inward versus outwarddirectionality around the circumference of the annular member 10. Theinward and outward extending channels 12, 14 extend radially withrespect to the longitudinal axis 11 of the annular member 10. Forexample, the centerline of each of the inward and outward extendingchannels 12, 14 creates a 90-degree angle with a line tangent to thediameter of the annular member 10 proximate the opening of the channel.The shape, in cross-section, of the inward and outward extendingchannels 12, 14 as depicted in FIG. 6A can include two substantiallyparallel and straight sides (defined by side wall 13 and side wall 15)that terminate at a rounded end 19. The rounded end 19 can have awidth/diameter greater than the width (w) of the corresponding inwardand outward extending channels 12, 14.

As described above, the annular member 10 and the elastic outer layer 50of the sheath 1 are designed to locally expand in a radial directionbetween a non-expanded and an expanded state as the prosthetic device112 is passed through the interior lumen of the sheath 1. FIG. 6Billustrates the annular member 10 and outer layer 50 in an expandedstate. The orientation and/or shape of the base members 20 and bridgemembers 30 of the annular member 10 change during expansion. Asillustrated in FIG. 6B, the base members 20 rotate, extend and/orelongate in a direction around the circumference of the annular member10 when transitioned to the expanded state. For example, the basemembers 20 can rotate with respect to the central axis of eachcorresponding base member 20. Similarly, the bridge members 30 alsochange in orientation and/or shape during expansion. In the non-expandedstate the bridge members 30 define an arcuate shape that flexes toincrease in radius/length upon expansion of the annular member 10. It isalso contemplated that the bridge members 30 can rotate, elongate and/orextend in a direction around the circumference of the annular member 10upon expansion. Upon expansion of the annular member 10, thedistance/spacing between adjacent base members 20 increases, wideningand changing the shape of the intervening inward and outward extendingchannels 12, 14 and increasing the overall diameter of the annularmember 10 and the outer layer 50. The wall thickness of the annularmember 10 is thinner at the bridge members 30 than compared to the basemembers 20. The decreased thickness at the bridge members 30 eases thebending of the bridge members 30 during expansion, lessening the chanceof fracture.

As illustrated in FIG. 6B, in the expanded state the contact surfaces 22provided on the base members 20 define the inner diameter of the annularmember 10. Likewise, the contact surface 24 defines the outer diameterof the annular member 10, and the corresponding inner diameter of theouter layer 50 in the expanded state. Contact surfaces 22 reduce thecontact surface area between the annular member 10 and the passingdevice, thereby lowering the coefficient of friction/resistance betweenthe annular member and the passing device.

As illustrated in FIGS. 2A, 3A, 4A, 5A, 6A and 7A, the size, shape,spacing and number of channels can vary. For example, the non-expandedembodiments of FIG. 2A and FIG. 7B have twenty four combined inward andoutward extending channels 12, 14. The non-expanded embodiments of FIG.3A and FIG. 6A have twenty combined inward and outward extendingchannels 12, 14, the non-expanded embodiment of FIG. 4A has eightcombined inward and outward extending channels 12, 14, and thenon-expanded embodiment of FIG. 5A has thirty six combined inward andoutward extending channels 12, 14.

Sheaths of the present disclosure can be used with various methods ofintroducing a prosthetic device into a patient's vasculature. Generally,during use, the expandable sheath 1 is passed through the skin ofpatient (usually over a guidewire) such that the distal end region ofthe expandable sheath 1 is inserted into a vessel, such as a femoralartery, and then advanced to a wider vessel, such as the abdominalaorta. The delivery apparatus 210 is then inserted through theexpandable sheath 1. The prosthetic device is then delivered to theimplantation site and implanted within the patient. During the advanceof the prosthetic device through the expandable sheath 1, the device andits delivery system exerts a radially outwardly directed force on theportion of the annular member 10, the annular member 10 exerts acorresponding radially outwardly directed force on the outer layer 50,causing both the annular member 10 and the outer layer 50 to expandlocally to accommodate the profile of the device. The expansion of theannular member 10 widens the longitudinally extending channels 12, 14 ofthe annular member and causes the movement of longitudinally extendingcontact surfaces 22, 24 toward the inner and outer surfaces 16, 18 ofthe annular member 10.

As the prosthetic device and its delivery system passes through theexpandable sheath 1, the expandable sheath 1 recovers. That is, itreturns to its original, non-expanded configuration. In someembodiments, this is facilitated by outer layer 50, which has a higherelastic modulus than annular member 10. The outer layer 50 moves thecontact surfaces 22, 24 of the annular member 10 away from the inner andouter surfaces after the passage of the prosthetic valve 212.

As described above, the expandable sheath 1 can be used to deliver,remove, repair, and/or replace a prosthetic device. In one example, theexpandable sheath 1 described above can be used to deliver a tissueheart valve to a patient. For example, a tissue heart valve (in acrimped state) can be placed on the distal end portion of an elongateddelivery apparatus and inserted into the sheath. Next, the deliveryapparatus and crimped heart valve can be advanced through the patient'svasculature to the treatment site, where the valve is implanted.

Beyond transcatheter heart valves, the expandable sheath 1 can be usefulfor other types of minimally invasive surgery, such as any surgeryrequiring introduction of an apparatus into a subject's vessel. Forexample, the expandable sheath 1 can be used to introduce other types ofdelivery apparatus for placing various types of intraluminal devices(e.g., stents, stented grafts, balloon catheters for angioplastyprocedures, etc.) into many types of vascular and non-vascular bodylumens (e.g., veins, arteries, esophagus, ducts of the biliary tree,intestine, urethra, fallopian tube, other endocrine or exocrine ducts,etc.).

FIGS. 7A-7C show cross-sections of an expandable sheath 1 including anannular member 10 and outer layer 50 similar to the annular member 10and outer layer 50 depicted in FIGS. 2A and 2B. FIG. 7A shows across-sections of an expandable sheath 1 during an intermediateprocessing step that includes a second material in addition to thematerial used to form the annular member 10. During processing, a tubeis coextruded containing a first material 60 and a second material 62.The first material 60 defines the annular member 10 discussed above. Thesecond material 62 does not adhere to the first material 60 and definesa first and second set of longitudinally extending ribbons 64, 66. Thesecond material 62 could be, or could incorporate, nylon, polyethyleneterephthalate, and/or polybutylene terephthalate, for example. The firstand second set of ribbons 64, 66 form the inward and outward extendingchannels 12, 14 of the annular member 10 during the extrusion process.The first set of ribbons 64 extends inwardly from the outer surface 16toward the inner surface 18 of the annular member 10, and the second setof ribbons 66 extends outwardly from the inner surface 18 toward theouter surface 16 of the annular member 10. Each ribbon of a selected setis positioned circumferentially between two ribbons of the other set.

In some embodiments, the second material 62 is a sacrificial material.For example, the ribbons 64, 66 of the second material 62 shown in FIG.7A are removed after coextrusion, exposing the longitudinally extendingchannels 12, 14 described above and as shown in the non-expandedembodiment of FIG. 7B.

However, some embodiments, such as the one shown in FIG. 6A, the firstmaterial 60 and second material 62 of the annular member 10 iscoextruded with a third material 68. This third material 68 is incontact with a portion of the first material 60 and a portion of thesecond material 62, and adheres to both the first and second materials60, 62. Because of the adherent third material 68, the second material62 is not removed. However, it still does not adhere to first material60. Instead, the third material 68 acts as a tie layer to hold the firstand second materials 60, 62 together during expansion of the annularmember 10. This eliminates the need to remove the ribbons 64, 66 of thesecond material 62 prior to use, while still allowing a widening of achannel between the non-adherent first 60 and second 62 materials duringthe expansion of the annular member 10. The retention of the secondmaterial 62 also increases the torque of the finished sheath, so that auser finds it easier to twist the sheath.

Some methods include a step of covering the annular member 10 with theouter layer 50 after coextrusion. As discussed above, the outer layer 50is formed of, or incorporates, a material with a higher elastic modulusthan the annular member 10.

FIG. 8 shows a perspective view of an example sheath 1. In this view,only the outer layer 50 is visible. The sheath 1 comprises a proximalend 3 and distal end 5 opposite the proximal end 3. The sheath 1 cancomprise a hemostasis valve inside the lumen of the sheath 1, at or nearthe proximal end 3. The sheath 1 can include a taper tube 70, a flaredproximal end. In some embodiments of the method of making, the tapertube 70 is added to the coextrusion. The addition of the second material62 will stabilize the coextrusion process and make it possible to add ataper tube 70 during extrusion. This is advantageous because it makes itpossible to eliminate the typical taper tube manufacturing steps offlaring (increasing the inner diameter of the sheath) and bonding(increasing the wall thickness after flaring).

Additionally, the sheath 1 can comprise a soft distal tip 80 at thedistal end 5. The soft tip 80 can be provided with a lower hardness thanthe other portions of the sheath 1. In addition to the method of makingthe expandable sheath described above, a method of making a distal tip80 of an expandable sheath 1 is demonstrated in the flow chart of FIG.9. The distal tip 80 can be formed on the annual member 10, outer layer50, or on the annular member 10 and outer layer 50 combined. The distaltip 80 of the expandable sheath 1 is softer and more elastic than themore proximal regions of the expandable sheath 1 because it must giveeasily when encountering tissue to reduce the possibility of injury andit must retain the ability to expand after the sealing (reflowing)process wherein the distal tip 80 is sealed to prevent blood fromentering the space between the annular member 10 and the outer layer 50.A first step to making the distal tip 80 is to attach a separate distaltube 82 to the distal end 5 of the expandable sheath 1, for example, byreflowing the materials together. Alternatively, the distal tube 82 canbe added to the distal end 5 of the sheath 1 via specialized extrusiontechnology. The distal tube 82 is formed of, or incorporates, a materialhaving greater elasticity than the remainder of the expandable sheath 1.One example material is Pebax.

Next, a portion of the distal tube 82 is pinched to create alongitudinally extending outer crease 84. The pinched portion is foldedover an outer surface of the distal tube 82 in a circumferentialdirection, creating a longitudinally extending flap 86 that is boundedby the outer crease 84 and a longitudinally extending inner crease 85.The inner crease 85 of the flap 86 is cut in a longitudinal directionfrom the distal edge 83 of the distal tube 82 to a proximally spacedpoint along the longitudinal axis of the distal tube 82. This creates alongitudinally extending inner edge 87. The flap 86 is cutcircumferentially from the outer crease 84 to the inner crease 85 at theproximally spaced point, such that the longitudinal cut of the innercrease 85 meets the circumferential cut at the proximally spaced point.The inner edge 87 of the flap is then extended in a circumferentialdirection around the outer surface 81 of the distal tube 82 and adheredto the outer surface 81.

In some embodiments, such as the one shown in FIG. 9, adhering the inneredge 87 of the flap 86 to the outer surface 81 can include covering thedistal end with an outer jacket 88, then reflowing the outer jacket 88with the distal tube 82 to form a sealed distal end. The outer jacket 88is also formed of highly elastic materials. One example material isNeusoft. This outer jacket 88 can, in some embodiments, be the samelayer as the outer layer 50 shown in FIGS. 2A-B. Because the flap 86 isunfolded and wrapped around the outer surface 81 before reflowing, thefinal wall thickness of the resulting distal tip varies minimally aroundits circumference.

Although the foregoing embodiments of the present disclosure have beendescribed in some detail by way of illustration and example for purposesof clarity and understanding, it will be apparent to those skilled inthe art that certain changes and modifications may be practiced withinthe spirit and scope of the present disclosure. It is intended that thescope of the present invention herein disclosed should not be limited bythe particular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

What is claimed is:
 1. An expandable sheath comprising: an elongated annular member comprising an inner surface and an outer surface, the annular member further including a bridge member extending between opposing first and second base members spaced around a circumference of the annular member, and an elastic outer layer extending over the annular member, the elastic outer layer having a lower lubricity than the annular member, wherein the expandable sheath is radially movable between an expanded state and a non-expanded state, wherein in the non-expanded state, the annular member includes a first longitudinally extending channel defined between the bridge member and the first base member, the first channel extending inwardly from the outer surface toward a longitudinal axis of annular member, and a second longitudinally extending channel defined between the bridge member and the second base member, the second channel extending outwardly from the inner surface away from the longitudinal axis of the annular member, wherein in the expanded state, the bridge member extends in a direction around the circumference of the annular member increasing a distance between the first and second base members, and wherein the elastic layer compresses the expanded annular member toward a non-expanded configuration.
 2. The expandable sheath of claim 1, wherein an expanded diameter of the annular member is greater than a non-expanded diameter of the annular member.
 3. The expandable sheath of claim 1, wherein an orientation of the first and second base members changes when the annular member moves between the expanded and non-expanded state.
 4. The expandable sheath of claim 3, wherein the orientation of the first and second base members rotates about a longitudinal axis of each of the respective base members when the annular member is moved between the expanded and non-expanded state of the annular member.
 5. The expandable sheath of claim 1, wherein the first and second base members include a contact edge defining an inner diameter of the annular member in the expanded state.
 6. The expandable sheath of claim 1, wherein the bridge member extends in a direction around a circumference of the annular member in the expanded state.
 7. The expandable sheath of claim 6, wherein the first and second base members extend in a direction around the circumference of the annular member in the expanded and non-expanded state, wherein at least a portion of the bridge member extends in a direction towards the longitudinal axis of annular member in the non-expanded state and around the circumference of the annular member in the expanded state.
 8. The expandable sheath of claim 1, wherein the first and second base members define a rectilinear shape in cross-section.
 9. The expandable sheath of claim 1, wherein the bridge member defines an S-shape in cross-section.
 10. The expandable sheath of claim 1, wherein the bridge member defines an arcuate shape in cross-section.
 11. An expandable sheath comprising: an elongated annular member radially movable between a non-expanded and expanded state, the annular member including: base members spaced around a circumference of the annular member, bridge members extending between opposing pairs of base members, and an elastic outer layer extending over the annular member, the elastic outer layer having a lower lubricity than the annular member, wherein in the non-expanded state the annular member includes inwardly and outwardly extending channels extending towards and away from a longitudinal axis of the annular member, respectively, the inwardly and outwardly extending channels defined between each of the opposing pairs of base members and each of the bridge members, wherein in the expanded state the bridge members extend in a direction around the circumference of the annular member such that a diameter of the annular member is increased and a spacing between opposing pairs of base members is increased from a non-expanded diameter and a non-expanded spacing when the annular member is in the non-expanded state, and wherein the elastic layer compresses the expanded annular member toward a non-expanded configuration.
 12. The expandable sheath of claim 11, wherein one of the inwardly extending channels and one of the outwardly extending channels is provided at opposing ends of a corresponding one of the bridge members.
 13. The expandable sheath of claim 11, wherein in the expanded state a depth of each of the inwardly and outwardly extending channels in a radial direction is decreased from a depth of each of the inwardly and outwardly extending channels in the non-expanded state.
 14. The expandable sheath of claim 11, wherein the base members include a first, second and third base member and the bridge members include a first and second bridge member, wherein the first bridge member extends between the first and second base members, wherein the second bridge member extends between the second and third base members. 